The mammalian heart is divided into four chambers. The superior or upper two chambers include the left and right atria. The right atrium is fluidly in communication with the venous system and carries deoxygenated blood. The left atrium receives oxygenated blood from the lungs and facilitates the movement of this blood into the left ventricle for pumping throughout the body.
The inferior vena cava (IVC) and the superior vena cava (SVC) generally lie, more or less, on a straight line from the diaphragm to the jugular vein. The right atrium forms a chamber that connects the two. Also draining into the right atrium is the coronary sinus. The right atrium lies anteriorly (in front of) and to the right side of the left atrium. The intra-atrial septum is a small area where the two atria are opposed to each other. The diameter of this structure is approximately 30-35 mm in the adult human. The intra-atrial septum is embryologically formed by the fusion of the septum secundum and the septum primum. In approximately 20% of adults, the septum is not fused and a potential passed therebetween exists known as a patent foramen ovale (PFO). Surrounding the intra-atrial septum, outside of the atrial walls, is the pericardial space. Anterior to the right atrium lies the aorta. Posterior to the left atrium lies the pulmonary veins.
For many procedures, e.g., mitral valvuloplasty, left atrial appendage closure, and left-sided arrhythmia ablation, it is desirable to enter or access the left atrium to effect the desired procedure while minimizing trauma to the patient. To non-operatively effect such access, one conventional approach involves puncturing the intra-atrial septum from the right atrial chamber to the left atrial chamber. For emerging procedures such as percutaneous valve repair and replacement, transeptal access to the left atrial chamber of the heart may allow for larger devices to be introduced into the venous system than can generally be introduced percutaneously into the arterial system.
The process of traversing from the right atrium and into the left atrium is called septostomy as the atrial septum is typically penetrated. Septostomy involves direct targeting of a small area of the atrial septum. If the targeted area is missed by the penetrating device, structures such as the aorta or the free wall of the atrium may be in danger of being penetrated. If such a penetration were to occur, serious injury or death to the patient could result. In fact, the most common serious complication of transeptal puncture is cardiac tamponade, a life-threatening condition resulting from misplacement of the transeptal puncture leading to bleeding into the pericardial space.
Interventional cardiologists typically gain access to the left atrium by performing a transeptal puncture using a special needle. The needle, which is hollow, is typically guided by utilizing fluoroscopy. However, fluoroscopy provides only two-dimensional imaging and does not preclude the possibility of the clinician inadvertently puncturing the septum in the wrong location. Some reports have shown that trans-esophageal echocardiography and intracardiac echocardiography can improve the safety of transeptal puncture; however these additional procedures are expensive, inconvenient, and add further risk to the procedure.
Perfecting the technique of transeptal puncture is very challenging for the clinician. Very few interventional cardiologists and electrophysiologists are currently skilled at this procedure. As difficult as it is to perform, it is more difficult to teach and relies upon both visual and tactile senses. Obtaining safe access to the left atrium remains a major obstacle to the growth of the technologies relating to the left atrium, e.g., left-sided arrhythmia mapping and ablation, atrial appendage closure in atrial fibrillation, percutaneous repair and replacement of heart valves, etc.